In the production of petroleum from oil wells, it is important to know the location of the liquid surface of the fluid in a well. This is particularly important in wells which must be pumped and which use a reciprocating rod that extends through the tubing. The information can be used to determine the maximum production rate of fluid from the well as well as to detect problems in the downhole pump and related equipment.
A principal technique for measuring the distance from the earth surface to the surface of the fluid has been echo ranging by the transmission of acoustic pulses down the well bore. This is generally done by use of an instrument called a "gun" which produces an acoustic pulse by a sudden expansion of gas or by the firing of a cartridge. An instrument is used which has a microphone that detects the acoustic activity within the well bore and is able to measure reflections from the tubing collars as well as a reflection from the liquid surface. By counting the reflections from the tubing collars, and knowing the length of each tubing joint, it is possible to calculate the depth to the fluid surface.
Although instruments of this type have been in use for many years, there is still a need for apparatus and procedures to better collect, analyze and display the information as well as to improve the ease of use of the instrument by the operator.